Worksheet 9, Section 104: Phase Changes And Latent Heat: Why

Worksheet 9 Section 104phase Changes And Latent Heat1 Why Is The Ev

Worksheet 9- Section 10.4 Phase Changes and Latent Heat 1. Why is the evaporation of sweat from the skin a cooling process? 2. What is latent heat, and how does it affect the temperature of a substance? 3. How much thermal energy must be removed from 0.96 kg of water at 0 °C to make ice cubes at 0 °C? (Latent heat of fusion of water = 335000 J/kg) 4. A portion of the vapor-pressure curve for water is shown in figure 10.28 above. Referring to the figure, estimate the pressure (in kPa) required for water to boil at 30 °C. 5. Using the vapor-pressure curve for water is shown in figure 10.28 above, estimate the temperature at which water boils when the pressure is 1.5 kPa.

Paper For Above instruction

The process of sweating plays a crucial role in human thermoregulation by facilitating cooling through evaporation. When sweat evaporates from the skin, it absorbs heat energy from the body, leading to a reduction in body temperature. This heat absorption is due to the latent heat of vaporization, which is the amount of energy required to convert a liquid into vapor without changing its temperature. Latent heat significantly impacts the thermal regulation as it allows the body to shed excess heat efficiently.

Latent heat is defined as the heat energy required to change the phase of a substance at constant temperature and pressure. It affects the temperature of a substance by enabling phase changes, such as melting, boiling, or vaporization, without altering the temperature during the process. When a substance absorbs latent heat, it undergoes a phase transition, which can regulate and stabilize its temperature despite heat input. Conversely, when latent heat is released during condensation or freezing, the temperature of the substance remains constant until the phase transition is complete.

To determine how much thermal energy must be removed from 0.96 kg of water at 0 °C to convert it into ice at 0 °C, we utilize the latent heat of fusion of water. The calculation involves multiplying the mass of water by the latent heat of fusion: Q = m × L. Substituting the known values gives Q = 0.96 kg × 335000 J/kg = 321,600 J. Therefore, 321,600 joules of energy must be removed to freeze the water at 0 °C.

The vapor-pressure curve for water (as shown in figure 10.28 in the referenced material) illustrates the relationship between temperature and vapor pressure. To estimate the pressure required for water to boil at 30 °C, one would locate 30 °C on the temperature axis of the curve and find the corresponding vapor pressure on the curve. Based on typical vapor-pressure data for water, the vapor pressure at 30 °C is approximately 4.25 kPa. This indicates that water boils at roughly 4.25 kPa when the temperature reaches 30 °C.

Similarly, to estimate the boiling temperature of water at a pressure of 1.5 kPa, one would locate 1.5 kPa on the vapor-pressure curve and find the temperature at this pressure point. From typical vapor-pressure data, water boils at approximately 10 °C when the pressure is around 1.5 kPa. This understanding is essential for understanding boiling points under different atmospheric or environmental pressures, which vary with altitude and other conditions.

In conclusion, the concepts of latent heat and vapor-pressure relationships are fundamental in thermodynamics and meteorology. They explain phenomena such as sweating and climate regulation and are critical in engineering applications involving phase change processes. Understanding how latent heat influences temperature changes during phase transitions enables better design of cooling systems, refrigeration, and weather prediction models.

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